I'm having the same problem. I get the pop up to say my iPad isn't registered but when I go to the registration page it says it is This comes after two nights when I've never been able to login during football. Very disappointing with the service of Virgin
Just spent 40 mins on phone to Virgin. Couldn't deregister my iPad from my iPad so that I could re-register it. Had to logon to laptop to de-register iPad and then tried to re-register it but that didn't solve the problem. In the end had to de- register iPad from the laptop and the re-register it from the iPad. In the meantime of course the programme I had wanted to watch was finished. Eh!!!
Sorry to hear that your unable to register your device to use TV Anywhere.
I can see on your account that there are no devices currently registered as you mentioned. On the device in question, go onto the app if its a mobile/tablet or sign into your account online if its a laptop/PC. Select a channel that is stream-able, it will have a wireless symbol next to the channel, when you click on watch now it should give you to option to register.
Try this and let me know how you get on and if the same message appears